Light source apparatus and light measuring apparatus

Abstract

To provide a light source apparatus capable of generating wavelength sweeping light at a high performance in a wavelength band other than a near-infrared wavelength band.SOLUTION: A light source apparatus 200 produces outgoing light L1 to irradiate a specimen. A pulse light source 210 generates near-infrared broad-band pulse light L0. A pulse stretcher 220 stretches the broad-band pulse light L0 in a time axis direction and generates near-infrared wavelength sweeping light L1a being a pulse train including a plurality of pulses having different center wavelengths. A wavelength conversion device 250 converts wavelengths of the near-infrared wavelength sweeping light L1a emitted from the pulse stretcher 220 and generates the outgoing light L1.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present disclosure relates to a light source device and an optical measurement device.

Background Art

[0002] Spectral analysis is widely used for component analysis and inspection of an object. In spectral analysis, irradiation light is irradiated onto the object, and the spectrum of the object light obtained as a result of the irradiation is measured. Then, based on the relationship between the spectrum of the object light and the spectrum of the irradiation light, optical characteristics such as reflection characteristics (wavelength dependency) or transmission characteristics can be obtained.

[0003] As one of the measurement methods of optical characteristics, wavelength sweep type spectroscopy is known. A wavelength sweep type spectroscope generates wavelength sweep light whose wavelength changes over time and irradiates the inspection target with the light. The wavelength sweep light is a pulse or a pulse train in which time and wavelength have a one-to-one relationship. Then, the time waveform of the light obtained by irradiating the inspection target with the wavelength sweep light is detected by a light receiver. The output waveform of the light receiver represents a spectrum in which the time axis corresponds to the wavelength.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Patent Document 1 discloses a light source device for a spectroscopic measurement device using wavelength sweep type spectroscopy. The conventional light source device uses SC light in a band of 900 nm to 1300 nm, and due to the configuration of an optical waveguide, an optical fiber, etc., the wavelength band that the light source device can generate is also limited to the near-infrared region of 900 nm to 1300 nm.

[0006] The present disclosure has been made in view of such problems, and an exemplary object of one of its aspects is to provide a light source device capable of generating wavelength-swept light with high efficiency in a wavelength band other than the near-infrared range.

Means for Solving the Problems

[0007] A light source device according to an aspect of the present disclosure generates emission light to be irradiated onto a sample. The light source device includes a pulse light source that generates near-infrared pulse light, a pulse stretcher that stretches the near-infrared pulse light in the time-axis direction to generate near-infrared wavelength-swept light, and a wavelength conversion device that converts the near-infrared wavelength-swept light emitted from the pulse stretcher to generate emission light.

[0008] In addition, any combination of the above components, as well as those obtained by mutually substituting the components and expressions of the present disclosure between methods, devices, systems, etc., are also effective as aspects of the present disclosure.

Effects of the Invention

[0009] According to an aspect of the present disclosure, wavelength-swept light in a wavelength band other than the near-infrared range can be generated with high efficiency.

Brief Description of the Drawings

[0010]

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Embodiments for Carrying Out the Invention

[0011] (Overview of Embodiments) The overview of some exemplary embodiments of the present disclosure will be described. This overview is for the purpose of providing a basic understanding of the embodiments as a prelude to the detailed description to follow, and simplifies and describes some concepts of one or more embodiments. It does not limit the scope of the invention or the disclosure. Also, this overview is not an all-inclusive overview of all possible embodiments and does not limit the essential components of the embodiments. For convenience, "one embodiment" may be used to refer to one embodiment (example or variation) or a plurality of embodiments (examples or variations) disclosed in this specification.

[0012] A light source device according to an aspect of the present disclosure generates emission light to be irradiated onto a sample. The light source device includes a pulse light source that generates near-infrared pulse light, a pulse stretcher that stretches the near-infrared pulse light in the time axis direction to generate near-infrared wavelength-swept light, and a wavelength conversion device that wavelength-converts the near-infrared wavelength-swept light emitted from the pulse stretcher to generate emission light. The near-infrared wavelength-swept light is a pulse train including a plurality of pulses having different center wavelengths.

[0013] Since the near-infrared region is used in optical communication and many highly efficient and reliable devices are provided, after generating wavelength-swept light in the near-infrared region and then wavelength-converting it, highly efficient wavelength-swept light can be generated in a band other than the near-infrared region.

[0014] In one embodiment, the light source device may further include a wavelength conversion laser. The wavelength conversion device may generate output light by a non-linear optical effect between the laser light generated by the wavelength conversion laser and the near-infrared wavelength swept light.

[0015] In one embodiment, the wavelength conversion laser may be a pulse laser that emits pulsed laser light.

[0016] In one embodiment, when the period of the pulse train is T1, the interval between a plurality of pulses is t1, the period of the pulsed laser light is T2, and m is a natural number, the relationship T2 = T1 + m × t1 may be satisfied. Thereby, wavelength swept light of a pulse train with an interval of T2 can be generated, and the change width of the wavelength per pulse can be set according to the value of m.

[0017] In one embodiment, the wavelength conversion laser may be a CW (Continuous Wave) laser that emits continuous light.

[0018] In one embodiment, the pulse stretcher may include a splitter that spatially splits near-infrared pulsed light according to wavelength and emits a plurality of split beams, a plurality of fibers that give different delays to the plurality of split beams, and a coupler that spatially multiplexes the plurality of beams output from the plurality of fibers and emits them as near-infrared wavelength swept light.

[0019] In one embodiment, the wavelength conversion device may include a PPLN (Periodically Poled Lithium Niobate) element.

[0020] In one embodiment, the period of the periodic inversion of the PPLN element may be chirped.

[0021] An optical measurement device according to one embodiment may include any of the above-described light source devices and a light receiving device that measures object light obtained by irradiating an object with the output light of the light source device.

[0022] (Embodiment) Hereinafter, the present disclosure will be described with reference to the drawings based on preferred embodiments. The same or equivalent components, members, and processes shown in each drawing are denoted by the same reference numerals, and redundant explanations will be omitted as appropriate. Further, the embodiments are illustrative rather than limiting the disclosure, and not all the features and combinations thereof described in the embodiments are necessarily essential to the disclosure.

[0023] The dimensions (thickness, length, width, etc.) of each member described in the drawings may be enlarged or reduced as appropriate for ease of understanding. Furthermore, the dimensions of a plurality of members do not necessarily represent their size relationships. On the drawing, even if a certain member A is drawn thicker than another member B, member A may be thinner than member B.

[0024] FIG. 1 is a block diagram showing the basic configuration of the optical measurement device 100 according to the embodiment. The optical measurement device 100 is a wavelength-sweeping spectrometer that measures the spectrum of the object OBJ, and mainly includes a light source device 200, a light receiving device 300, and an arithmetic processing device 400. In some figures, the light source device 200, the light receiving device 300, etc. may be shown simply as boxes, but this is not intended to mean that the members constituting each are housed in a single housing.

[0025] The light source device 200 irradiates the object OBJ with wavelength-sweeping light L1 whose wavelength changes over time. The wavelength-sweeping light L1 has a one-to-one correspondence between time and wavelength. This is referred to as the wavelength-sweeping light L1 having "wavelength uniqueness".

[0026] FIG. 2 is a diagram showing the wavelength-sweeping light L1. The upper part of FIG. 2 shows the intensity (time waveform) I WS (t) of the wavelength-sweeping light L1, and the lower part shows the time change of the wavelength λ of the wavelength-sweeping light L1. In this example, the wavelength-sweeping light L1 is a single pulse of light, and the main wavelength is λ1 at the leading edge and λ n at the trailing edge, and the wavelength changes from λ1 to λ within one pulse nIt changes over time among them. In this example, the wavelength-swept light L1 is a positive chirp pulse (λ1 > λ n ) whose frequency increases with time, or in other words, whose wavelength becomes shorter with time. Note that the wavelength-swept light L1 may be a negative chirp pulse whose wavelength becomes longer with time (λ1 < λ n ). As will be described later, the wavelength-swept light L1 may be a pulse train.

[0027] Returning to FIG. 1. The light receiving device 300 receives the light (object light) L2 obtained as a result of irradiating the object OBJ with the wavelength-swept light L1. The object light L2 may be reflected light or transmitted light. The light receiving device 300 includes light sensors 302 and 304 such as photodiodes, an A / D converter 310, an optical system (not shown), and the like. The object light L2 is detected by the light sensor 302. A part of the wavelength-swept light L1 generated by the light source device 200 is taken out as reference light L3 in a separate path using an optical element such as a beam splitter and is detected by the light sensor 304.

[0028] The A / D converter 310 converts the output signals S2 and S3 of the light sensors 302 and 304 into digital signals D2 and D3, respectively. The time waveform I OBJ (t) of the object light L2 indicated by the digital signal D2 and the time waveform I REF (t) of the reference light L3 indicated by the digital signal D3 are taken into the arithmetic processing unit 400.

[0029] In the wavelength-swept spectroscopy, the time and wavelength in the wavelength-swept light L1 have a one-to-one correspondence. This correspondence naturally also exists in the reference light L3 and is also inherited by the object light L2. Using this correspondence between time and wavelength, the arithmetic processing unit 400 converts the time waveform I OBJ (t) of the object light L2 into the spectrum I OBJ (λ) in the frequency domain. Further, the arithmetic processing unit 400 converts the time waveform I REF (t) of the reference light L3 into a spectrum and appropriately scales it to calculate the reference spectrum I REF (λ).

[0030] The processing of the arithmetic processing unit 400 is not particularly limited. As an example, the arithmetic processing unit 400 calculates the transmittance T(λ) of the object OBJ based on the reference spectrum I REF (λ) and the spectrum I OBJ (λ) of the object light L2. The same applies to the reflectance R(λ). T(λ) = I OBJ (λ) / I REF (λ) R(λ) = I OBJ (λ) / I REF (λ)

[0031] When the wavelength-swept light L1 has high stability, the spectrum of the wavelength-swept light L1 may be measured in advance and used as the reference spectrum I REF (λ).

[0032] FIG. 3 is a diagram for explaining the spectroscopy by the optical measurement device 100 of FIG. 1. As described above, since the wavelength-swept light L1 has a one-to-one correspondence between time t and wavelength λ, its time waveform I REF (t) can be converted into the spectrum I REF (λ) in the frequency domain.

[0033] The time waveform I OBJ (t) of the object light L2 also has a one-to-one correspondence between time t and wavelength λ. Therefore, the arithmetic processing unit 400 can convert the waveform I OBJ (t) of the object light L2 indicated by the output of the light receiving device 300 into the spectrum I OBJ (λ) of the object light L2.

[0034] The arithmetic processing unit 400 can calculate the transmittance spectrum T(λ) of the object OBJ based on the ratio I OBJ (λ) and I REF (λ) of the two spectra I OBJ (λ) / I REF (λ).

[0035] Assume that the relationship between the wavelength λ and the time t in the wavelength-swept light L1 is represented by a function λ = f(t). Most simply, the wavelength λ changes linearly with respect to the time t according to a linear function. The time waveform I OBJ (t) of the object light L2 decreases at a certain time t x , the transmission spectrum T(λ) means that it has an absorption spectrum at the wavelength λ x = f(t x ).

[0036] Note that the processing in the arithmetic processing unit 400 is not limited to this. The ratio T(t) = I OBJ (t) / I REF (t) of two time waveforms I OBJ (t) and I REF (t) is calculated, and then the variable t of this time waveform T(t) is converted to λ to calculate the transmission spectrum T(λ).

[0037] The above is the basic configuration and operation of the optical measurement device 100. Next, the configuration of the light source device 200 will be described.

[0038] FIG. 4 is a diagram showing the light source device 200 according to the embodiment. In this embodiment, the light source device 200 is configured to be able to generate the wavelength-swept light L1 in a wavelength band other than the near-infrared. The light source device 200 includes a pulse light source 210, a pulse stretcher 220, a wavelength conversion device 250, and a wavelength conversion laser 260.

[0039] The pulse light source 210 emits a broadband pulse light L0 having a broadband continuous spectrum in the near-infrared. The broadband pulse light L0 is SC (Super Continuum) light, and the spectrum of the broadband pulse light L0 is continuous over a wavelength range of at least 10 nm, preferably 100 nm, more preferably 400 nm, for example, in the range of 900 nm to 1300 nm.

[0040] For example, the pulse light source 210 may include an ultrashort pulse laser and a nonlinear element. Examples of the ultrashort pulse laser include a gain-switching laser, a microchip laser, and a fiber laser.

[0041] The nonlinear element further broadens the spectral width of the ultrashort pulses generated by the ultrashort pulse laser by a nonlinear phenomenon. A fiber is suitable as the nonlinear element, and for example, a photonic crystal fiber or other nonlinear fibers can be used. The single-mode case is preferable as the mode of the fiber, but a multimode fiber can also be used as long as it exhibits sufficient nonlinearity. The broadband pulsed light L0 output from the nonlinear element has a pulse width on the order of femtoseconds to nanoseconds.

[0042] As the pulse light source 210, other broadband pulse light sources such as an SLD (Superluminescent Diode) light source may be used. Alternatively, it is preferable to use a light source with high spatial coherence for coupling to the fiber.

[0043] The pulse stretcher 220 stretches the broadband pulsed light L0 in the time axis direction to generate near-infrared wavelength-swept light L1a. The wavelength of the wavelength-swept light L1a changes with time toward the wavelength λa1 to λa n

[0044] The wavelength conversion device 250 wavelength-converts the near-infrared wavelength-swept light L1a emitted from the pulse stretcher 220 to generate output light that is wavelength-swept light L1 outside the near-infrared range. The wavelength of the wavelength-swept light L1 changes with time toward λ1 to λ n

[0045] In this embodiment, a wavelength conversion laser 260 is provided for wavelength conversion. The wavelength conversion laser 260 is a pulse laser or a CW laser and generates laser light L1b with a wavelength of λb. As the wavelength conversion laser 260, a solid-state laser, a fiber laser, or a semiconductor laser can be used. ​​

[0046] The wavelength conversion device 250 generates the output light L1 by the nonlinear optical effect between the laser light L1b generated by the wavelength conversion laser 260 and the near-infrared wavelength swept light L1a.

[0047] As the nonlinear optical effect in the wavelength conversion device 250, sum frequency generation (SFG), differential frequency generation (DFG), optical parametric generation (OPG), and four-wave mixing (FWM) can be utilized.

[0048] λ i is determined according to λa i and λb. Let the frequency corresponding to each wavelength λ be ω. When using SFG, ω i = ωa i + ωb holds. When using DFG, ω i = ωa i - ωb holds.

[0049] The type of the nonlinear optical effect and the wavelength λb of the laser light L1b can be determined based on the wavelength band λ1~λ of the required wavelength swept light L1. The wavelength λb of the laser light L1b is preferably, for example, wavelengths 1064 nm, 1300 nm, 1550 nm. n

[0050] As the wavelength conversion device 250, a periodically poled lithium niobate (PPLN) element or a periodically poled MgO doped lithium niobate (PPMgO) element in bulk or waveguide form, etc., which uses a periodically reversed polarization module, can be used. Since the periodically reversed polarization module can usually convert only a wavelength range of several nm to several tens of nm, in order to achieve broadband wavelength conversion, the periodically reversed polarization module may adopt a structure in which the period of the periodically reversed polarization gradually changes (chirps). Alternatively, a multiple grating in which a single PPLN element contains multiple periods of PPLN, or a fan-out grating in which a single PPLN element contains sectorially reversed polarization, can also be used as an element for achieving broadband wavelength conversion.

[0051] FIG. 5 is a diagram for explaining wavelength conversion in the wavelength conversion device 250.

[0052] · Mid-infrared to far-infrared wavelength band Difference frequency generation DFG of the laser light L1b and the wavelength-swept light L1a can be used, and as the wavelength conversion laser 260, an Er fiber laser with λb = 1550 nm can be used. In this case, the mid-infrared band with a wavelength of 2 μm to 4 μm and the far-infrared band with a wavelength of 4 μm to 8 μm can be covered.

[0053] Optical parametric generation (OPG) or four-wave mixing (FWM) can also be used to generate the mid-infrared to far-infrared wavelength-swept light L1.

[0054] · Visible region Sum frequency generation SFG of the laser light L1b and the wavelength-swept light L1a can be used, and as the wavelength conversion laser 260, a solid-state laser (Nd:YAG, Nd:YVO4) with λb = 1064 nm, or a Yb fiber laser with λb = 1030 nm can be used, and the wavelength range of 450 nm to 800 nm can be covered.

[0055] · Ultraviolet region After generating wavelength-swept light in the visible region using SFG, wavelength-swept light L1 in the ultraviolet region may be generated using second harmonic generation (SHG).

[0056] The above is the configuration of the light source device 200. Next, the advantages of the light source device 200 will be described. The advantages of the light source device 200 will become clear by comparison with the comparative technology.

[0057] In the comparative technology, the configuration of the light source device described in Patent Document 1 is directly replaced in a wavelength region other than the near-infrared. That is, the light source device includes an SC light source in a target wavelength band other than the near-infrared, an AWG, and an optical fiber that function in this wavelength band.

[0058] For example, consider applying the comparative technology described in Patent Document 1 to a visible wavelength band shorter than the near-infrared region. In this case, SC light can be generated relatively easily using wavelength conversion, short-pulse lasers, etc. On the other hand, it is known that when fabricating an optical waveguide at a short wavelength, the influence of light scattering due to abnormal shapes of the waveguide itself becomes large (the fourth power of the wavelength), and the loss due to scattering becomes extremely large. Although research on small microscope devices using optical waveguides has been carried out, it is known that large optical losses in the visible wavelength region of optical waveguides are one of the main technical issues, and the development of a new manufacturing process for optical waveguides is required. Also, since the core diameter of a single-mode optical fiber is approximately proportional to the wavelength, for an optical fiber with a core diameter of φ9.5μm used in the 1.5μm wavelength band, the core diameter of an optical fiber for the 400nm wavelength band is about φ3μm. Therefore, the requirements for adhesion of each component, mechanical accuracy, assembly tolerance, and stability become extremely strict. Furthermore, it is known that aging deterioration is severe in the ultraviolet wavelength band below 400nm, and development is required from the material itself of the optical fiber and optical waveguide.

[0059] Consider applying the comparative technique described in Patent Document 1 to the mid-infrared wavelength band, which has a longer wavelength than the near-infrared region. SC light can be relatively easily generated by wavelength conversion technology, etc. However, at mid-infrared wavelengths, the absorption of molecular vibrations is strong, and the absorption due to impurities contained in SiO2 used in optical fibers and waveguides is extremely large. Also, since the development of materials that can obtain the optimal dispersion for guiding waves has not progressed, it is difficult to fabricate optical waveguide devices in the mid-infrared region. That is, it is necessary to start from the development of materials for the optical waveguide and optical fiber itself.

[0060] In this embodiment, near-infrared wavelength-swept light L1a is generated by a pulse light source 210 and a pulse stretcher 220 surrounded by a broken line 201 in FIG. 4. For the part of this broken line 201, since a known technique with proven results can be used, the development of a new device is not necessary. And after generating the near-infrared wavelength-swept light L1a, the wavelength of the wavelength-swept light L1a can be wavelength-converted by utilizing the nonlinear optical effect to generate the wavelength-swept light L1 in the target wavelength band.

[0061] This disclosure is understood as the block diagram of FIG. 4, or extends to various devices and methods derived from the above description, and is not limited to a specific configuration. Hereinafter, in order to help understand and clarify the essence and operation of this disclosure and the present invention, rather than narrowing the scope of this disclosure, more specific configuration examples and embodiments will be described.

[0062] (Example 1) FIG. 6 is a diagram showing a light source device 200A according to Example 1. In this example, the wavelength-swept light L1a generated by the pulse stretcher 220A is a pulse train including a plurality of n pulses with different center wavelengths. The wavelength conversion laser 260A is a CW laser.

[0063] FIG. 7 is a diagram showing a configuration example of the pulse stretcher 220A that generates the pulse train of the wavelength-swept light L1a. The pulse stretcher 220A includes a splitter 222, a delay line 228, and a coupler 232.

[0064] The pulse stretcher 220A receives the broadband pulsed light L0 and converts it into the wavelength-swept light L1a of a pulse train.

[0065] The splitter 222 includes an arrayed waveguide grating (AWG) 224 and a lens 226. The lens 226 condenses the broadband pulsed light L0 emitted from the pulse light source 210 onto the incident end of the AWG 224.

[0066] The AWG 224 spatially divides the broadband pulsed light L0 into a plurality of n beams (referred to as divided beams) L01 to L0 n according to the wavelength and outputs them. The number of divisions (number of channels) n is equal to the number of fibers 230. The number of channels n can be, for example, 4, 8, 16, 32, 64, 128, etc. The wavelength of the i-th (1 ≤ i ≤ n) divided beam is denoted as λ i Note that since the divided beams L01 to L0 n each have a certain wavelength width rather than a single spectrum, λ i is not a single wavelength but is used for convenience to represent the wavelength band that L0 i has, and in some cases, is used to represent the center wavelength of the wavelength band. The divided beams L01 to L0 n output from the AWG 224 are guided to the delay line 228.

[0067] The delay line 228 gives different delays to the plurality of divided beams L01 to L0 n The delay line 228 may include a plurality of fibers 230_1 to 230_n with different lengths. The i-th divided beam L0 i is coupled to the incident end of the corresponding fiber 230_i.

[0068] Assume that the broadband pulsed light L0 before division is a positive chirp pulse (up-chirp pulse) in which the frequency increases (the wavelength becomes shorter) with time. That is, the component of the longest wavelength λ1 is included in the leading edge of the pulse, and the component of the shortest wavelength λ n is included in the trailing edge of the pulse.

[0069] The plurality of fibers 230_1 to 230_n have different lengths l1 to l n If λ1 is the longest wavelength and λ n is the shortest wavelength, in order to make the wavelength-swept light L1 the same positive chirp pulse as the broadband pulsed light L0, it is only necessary to satisfy the relationship of 11 < l2 < … < l n For example, when n = 20, the lengths l1 to l n of the fibers 230 may increase in 1 m increments from 1 m to 20 m.

[0070] The fibers 230_1 to 230_n do not necessarily have different group delay characteristics for each wavelength, and the same fiber (a fiber of the same core / clad material) can be used.

[0071] The coupler 232 spatially overlaps and emits a plurality of split beams with different delays imparted by the delay line 228. Similar to the splitter 222, the coupler 232 includes an AWG 234 and a lens 236.

[0072] Returning to FIG. 6. Each pulse included in the wavelength-swept light L1a of the pulse train and the CW laser light L1b interact with the wavelength conversion device 250, thereby generating the wavelength-swept light L1 of the pulse train. The central wavelength of each pulse included in the wavelength-swept light L1 of the pulse train is λ1, λ2, … λ n and the time interval between each pulse of the wavelength-swept light L1 is substantially equal to the time interval between each pulse of the wavelength-swept light L1a. Thus, according to the light source device 200A in FIG. 6, the wavelength-swept light L1 of the pulse train can be generated.

[0073] (Embodiment 2) FIG. 8 is a diagram showing a light source device 200B according to Embodiment 2. Also in this embodiment, the wavelength-swept light L1a generated by the pulse stretcher 220A is a pulse train including a plurality of n pulses with different central wavelengths.

[0074] The wavelength-converting laser 260B is a pulsed laser. The pulses of the laser beam L1b generated by the wavelength-converting laser 260B are controlled in timing so as to enter the wavelength-converting device 250 simultaneously with one of the plurality of pulses included in the wavelength-swept beam L1a. Note that the relationship between the pulse width of the laser beam L1b and the pulse width of each pulse of the wavelength-swept beam L1a is not particularly limited. The wavelength-converting laser 260B may include a plurality of pulsed lasers operating in different phases. Further, the seed laser of the pulse light source 210 may be diverted and used as the wavelength-converting laser 260B.

[0075] FIG. 9 is a diagram for explaining an operation example of the light source device 200B in FIG. 8. The wavelength-converting laser 260B generates the laser beam L1b at intervals equal to the interval t1 of the pulses generated by the pulse stretcher 220A.

[0076] At this time, the wavelength-swept beam L1 emitted from the wavelength-converting device 250 becomes a pulse train with a period t1, and the wavelength of each pulse changes as λ1, λ2, λ3,....

[0077] FIG. 10 is a diagram for explaining an operation example of the light source device 200B in FIG. 8. The wavelength-converting laser 260B emits pulses at a constant period T2. Let the period of the pulse train of the wavelength-swept beam L1a generated by the pulse stretcher 220A be T1, and the interval of a plurality of n pulses included therein be t1. The period T2 of the pulsed laser beam L1b generated by the wavelength-converting laser 260B is determined so as to satisfy the following relational expression. T2 = T1 + t1

[0078] At this time, the wavelength-swept beam L1 emitted from the wavelength-converting device 250 becomes a pulse train with a period T2, and the wavelength of each pulse changes as λ1, λ2, λ3,....

[0079] Generally, the period T2 of the pulsed laser beam L1b generated by the wavelength-converting laser 260B can be determined so as to satisfy the following relational expression. T2 = T1 + m × t1 m is a natural number. According to m, the change width of the wavelength for each pulse of the wavelength-swept light L1 can be set.

[0080] FIG. 11 is a diagram for explaining another operation example of the light source device 200B in FIG. 8. The period T2 of the wavelength conversion laser 260B is equal to the period T1 of the wavelength-swept light L1a. T2 = T1

[0081] The timing Δt of the pulsed laser light L1b generated by the wavelength conversion laser 260B is variable relative to the pulse train of the wavelength-swept light L1a. In the state where Δt = 0, the wavelength-swept light L1 becomes a pulse train of wavelength λ1, and in the state where Δt = t1, the wavelength-swept light L1 becomes a pulse train of wavelength λ2. Generally speaking, in the state where Δt = t1×i, the wavelength-swept light L1 is a pulse train of wavelength λ (i+1) . Thus, by increasing Δt for every m pulses (m is a natural number) of the laser light L1b, it is possible to generate the wavelength-swept light L1 in which m pulses of wavelength λ1, m pulses of wavelength λ2, m pulses of wavelength λ3,... are successively connected. Alternatively, if Δt is continuously fixed, it is possible to continuously generate pulses of an arbitrary wavelength.

[0082] Regarding the embodiments according to the present disclosure, specific terms have been used for explanation, but this explanation is merely an exemplification for the purpose of assisting understanding and does not limit the present disclosure or the scope of the claims. The scope of the present invention is defined by the scope of the claims, and thus, embodiments, examples, and modifications not described herein are also included in the scope of the present invention.

Explanation of Reference Numerals

[0083] 100 Optical measurement device 300 Light receiving device 400 Arithmetic processing device 200 Light source device 210 Pulse light source 220 Pulse stretcher 250 Wavelength conversion device 260 Wavelength conversion laser 222 Splitter 224 AWG 226 lens 228 delay line 230 fiber 232 coupler 234 AWG 236 lens L0 broadband pulsed light L1a wavelength-swept light L1b laser light L1 wavelength-swept light L2 object light L3 reference light

Claims

1. A light source device for generating emission light to be irradiated on a sample, comprising: a pulse light source for generating near-infrared pulse light; a pulse stretcher for stretching the near-infrared pulse light in the time axis direction to generate near-infrared wavelength-swept light; a wavelength conversion device for wavelength-converting the near-infrared wavelength-swept light emitted from the pulse stretcher to generate the emission light; The light source device is characterized in that the near-infrared wavelength-swept light is a pulse train including a plurality of pulses having different center wavelengths.

2. The light source device according to claim 1, further comprising a laser for wavelength conversion, wherein the wavelength conversion device generates the emission light by the interaction between the laser light generated by the laser for wavelength conversion and the near-infrared wavelength-swept light.

3. The light source device according to claim 2, wherein the laser for wavelength conversion is a pulse laser that emits pulsed laser light.

4. When the period of the pulse train is T1, the interval between the plurality of pulses is t1, the period of the pulsed laser light is T2, and m is a natural number, T2 = T1 + m × t1 The light source device according to any one of claims 1 to 3, characterized in that the relationship is satisfied.

5. The light source device according to claim 2, wherein the laser for wavelength conversion is a CW (Continuous Wave) laser that emits continuous light.

6. The pulse stretcher includes: a splitter for spatially splitting the near-infrared pulse light according to wavelength and emitting a plurality of split beams; a plurality of fibers for imparting different delays to the plurality of split beams; a coupler for spatially multiplexing the plurality of beams output from the plurality of fibers and emitting the multiplexed beam as the near-infrared wavelength-swept light. The light source device according to any one of claims 1 to 3, characterized in that it includes the above components.

7. The light source device according to any one of claims 1 to 3, wherein the wavelength conversion device includes a PPLN (Periodically Poled Lithium Niobate) element.

8. The light source device according to claim 7, wherein the period of the periodic inversion of the PPLN element is chirped.

9. A light measurement device, comprising: the light source device according to any one of claims 1 to 3; a light receiving device for measuring object light obtained by irradiating an object with the emission light of the light source device. The light measurement device is characterized in that it includes the above components.

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